Cuprous oxide (Cu 2 O) nanostructures have been synthesized by anodic oxidation of copper through a simple electrolysis process employing plain water (with ionic conductivity ∼6 µS/m) as an electrolyte. No special electrolytes, chemicals, and surfactants are needed. The method is based on anodization pursuant to the simple electrolysis of water at different voltages. Platinum was taken as cathode and copper as anode. The applied voltage was varied from 2 to10 V. The optimum anodization time of about 1 h was employed for each case. Two different types of Cu 2 O nanostructures have been found. One type was delaminated from copper anode and collected from the bottom of the electrochemical cell and the other was located on the copper anode itself. The nanostructures collected from the bottom of the cell are either nanothreads embodying beads of different lengths and diameter ∼10-40 nm or nanowires (length ∼600-1000 nm and diameter ∼10-25 nm). Those present on the copper anode were nanoblocks with a preponderance of nanocubes (nanocube edge ∼400 nm). The copper electrode served as a sacrificial anode for the synthesis of different nanostructures. A tentative mechanism for the formation of Cu 2 O nanostructures has been suggested. The present work represents the first such attempt where Cu 2 O nanostructures were formed under the oxidation induced by as simple a process as electrolysis of plain water. Both anodization potential and time influence the morphology of nanostructures of Cu 2 O. Thus, nanothreads are formed at 6 V during 15-30 min, whereas nanowires result when anodization time is extended to 45-60 min. Also two different types of Cu 2 O nanostructures, one which is present in the solution (nanothreads and nanowires) and the other which is located on the copper anode (nanocubes), are synthesized in the same electrolysis run. The optical band gap as calculated from the UV-visible absorption spectra of the nanothreads and nanowires corresponds to 2.61 and 2.69 eV, respectively, which is larger than the known band gap (2.17 eV) of bulk Cu 2 O.

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